In a three-phase electric induction motor, an electrical current conducted through windings of a stationary portion of the motor produce a changing magnetic field, with the changing magnetic field in turn causing the rotor to rotate. In a permanent magnet synchronous motor, permanent magnets are attached to different portions of the rotor. An application of a three-phase alternating current (AC) voltage to the stator windings induces a changing magnetic field around the rotor, with the force of the opposing magnetic field of the permanent magnets causing the rotor shaft to rotate. Torque provided by a rotating shaft then can be harnessed and directed as needed for performing useful mechanical work within a system, for example by selectively connecting the rotor shaft to a transmission output shaft of a vehicle.
In a hybrid vehicle transmission in particular, one or two electric motor/generators can be used alone or selectively in conjunction with an internal combustion engine, a fuel cell, or other energy source in order to propel the vehicle. Such electric motor/generators are typically powered by a relatively high level of AC voltage. To ensure proper operation of the motor/generators, as well as to optimize fuel economy of the vehicle, a motor controller is provided which can perform various measurements and/or diagnostics of the electrical and mechanical systems aboard the vehicle. However, typical motor control methods may be less than optimal for detecting certain performance issues that are unique to multi-phase AC motors, such as a permanent magnet synchronous motor.